<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title>按钮式下拉菜单</title>
    <link href="bootstrap.min.css" rel="stylesheet">
    <link rel="stylesheet" href="http://cdn.bootcss.com/bootstrap/3.3.4/css/bootstrap.min.css">
</head>
<body>
    <div class="container">
        <div class="btn-group">
            <button type="button" class="btn btn-info dropdown-toggle" data-toggle="dropdown">
                下拉菜单
                <span class="caret"></span>

            </button>
            <ul class="dropdown-menu" role="menu">
                <li><a herf="#">第一个</a></li>
                <li><a herf="#">第二个</a></li>
                <li><a herf="#">第三个</a></li>
            </ul>
        </div>
        <br/>
        <br/>
        <div class="btn-group">
            <button type="button" class="btn btn-info" data-toggle="dropdown">
                下拉菜单
            </button>
            <button type="button" class="btn btn-info dropdown-toggle" data-toggle="dropdown">
                <span class="caret"></span>
            </button>
            <ul class="dropdown-menu" role="menu">
                <li><a herf="#">第一个</a></li>
                <li><a herf="#">第二个</a></li>
                <li><a herf="#">第三个</a></li>
            </ul>

        </div>
        <!--按钮尺寸-->
        <br/>
        <br/>
        <div class="btn-group">
            <button type="button" class="btn btn-info btn-sm" data-toggle="dropdown">
                下拉菜单
            </button>
            <button type="button" class="btn btn-info btn-sm dropdown-toggle" data-toggle="dropdown">
                <span class="caret"></span>
            </button>
            <ul class="dropdown-menu" role="menu">
                <li><a herf="#">第一个</a></li>
                <li><a herf="#">第二个</a></li>
                <li><a herf="#">第三个</a></li>
            </ul>

        </div>

        <!--弹出方向-->
        <br/>
        <br/>
        <div class="btn-group dropup">
            <button type="button" class="btn btn-info btn-sm" data-toggle="dropdown">
                下拉菜单
            </button>
            <button type="button" class="btn btn-info btn-sm dropdown-toggle" data-toggle="dropdown">
                <span class="caret"></span>
            </button>
            <ul class="dropdown-menu" role="menu">
                <li><a herf="#">第一个</a></li>
                <li><a herf="#">第二个</a></li>
                <li><a herf="#">第三个</a></li>
            </ul>

        </div>
    </div>
    <script src="jquery-1.11.1.js"></script>
    <script src="bootstrap.min.js"></script>
</body>
</html>